mfd: ssbi: Remove platform data structs and hide ssbi type enum

The ssbi driver assumes that the device is DT based. Remove the
platform data structs that will never be used and hide the enum
in the only C file that uses it.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>